1. Field of the Invention
The present invention relates generally to a method and an apparatus for exchanging information between evolved Node Bs (eNBs) in a cellular mobile communication system including a plurality of eNBs, and more particularly, to a method and an apparatus for the efficient exchange of interference and channel information between eNBs in a Coordinated Multi-Point (CoMP) in which a plurality of eNBs support downlink transmission of a User Equipment (UE) in cooperation with each other.
2. Description of the Prior Art
From the early stage of providing voice-oriented services, mobile communication systems have evolved into high-speed, high-quality wireless packet data communication systems which provide data and multimedia services. Various mobile communication standards such as High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Long Term Evolution (LTE), and Long Term Evolution-Advanced (LTE-A) of the 3rd Generation Partnership Project (3GPP), High Rate Packet Data (HRPD) of the 3rd Generation Partnership Project-2 (3GPP2), and IEEE 802.16 have recently been developed to support high-speed and high-quality wireless packet data communication services.
The LTE system, which is a system developed to efficiently support high speed wireless packet data transmission, can maximize the capacity of a wireless system through the use of various wireless access technologies. Further, the LTE-A system, which is an advanced wireless system that has evolved from the LTE system, has enhanced data transmission capabilities compared to the LTE system.
The existing 3rd generation wireless packet data communication systems, such as HSDPA, HSUPA and HRPD, use technologies of an Adaptive Modulation and Coding (AMC) scheme and a channel-sensitive scheduling scheme to improve the transmission efficiency. The AMC scheme and the channel-sensitive scheduling scheme allow a transmitter to apply an appropriate modulation and coding technique at a time point determined to be most efficient, based on partial channel state information fed back from a receiver.
In a wireless packet data communication system employing the AMC scheme, a transmitter can adjust the amount of transmission data depending on a given channel state. That is, when the channel state is performing less than optimal, the transmitter can reduce the amount of transmission data to adjust the reception error probability to a desired level. In contrast, when the channel state is performing optimally, the transmitter can increase the amount of transmission data to achieve efficient transmission of a large quantity of information, while adjusting the reception error probability to a desired level.
In a wireless packet data communication system employing the channel-sensitive scheduling-based resource management method, the transmitter selectively provides a service performing optimally to a user among a plurality of users, thus increasing the system capacity compared to methods which assign a channel to one user and provide a service to the user with the assigned channel. Such a capacity increase is referred to as a multi-user diversity gain. The AMC scheme, when used together with a Multiple Input Multiple Output (MIMO) transmission scheme, may include a function of determining the rank or the number of spatial layers of a transmission signal. Here, a wireless packet data communication system employing the AMC scheme determines an optimal data rate in consideration of not only a coding rate and a modulation scheme, but also the number of layers for transmission using MIMO.
It is generally known that the Orthogonal Frequency-Division Multiple Access (OFDMA) scheme, compared to the Code-Division Multiple Access (CDMA) scheme, can increase system capacity. One of the several causes bringing about the system capacity increase in the OFDMA scheme is that the OFDMA scheme can perform scheduling on the frequency axis (e.g., frequency domain scheduling). Although a capacity gain is acquired according to the time-varying channel characteristic using the channel-sensitive scheduling method, it is possible to obtain a higher capacity gain with use of the frequency-varying channel characteristic. Recently, intensive research is being conducted to replace CDMA, the multiple access scheme used in the 2nd and 3rd generation mobile communication systems, with OFDMA in the next generation system. Further, 3GPP and 3GPP2 have started their standardizations on the evolved systems using OFDMA.
FIG. 1 illustrates a radio frame structure of an LTE-A system.
Referring to FIG. 1, one radio frame is configured by 10 sub-frames and each sub-frame is configured by two slots. Within one radio frame, the sub-frames have indexes of 0 to 9 and the slots have indexes of 0 to 9 (#0 to #19).
FIG. 2 illustrates a cellular mobile communication system according to the prior art in which a transmission/reception antenna is located at the center of each cell.
Referring to FIG. 2, in a cellular mobile communication system including a plurality of cells, a particular UE receives a mobile communication service provided using various methods described above from one cell selected in a long time period (e.g., semi-static period). For example, it is assumed that a cellular mobile communication system is configured by three cells including a cell 100, a cell 110, and a cell 120. Further, it is also assumed that the cell 100 provides a mobile communication service to a UE 101 and a UE 102 located within the cell 100, the cell 110 provides a mobile communication service to a UE 111 located within the cell 110, and the cell 120 provides a mobile communication service to a UE 121 located within the cell 120.
Among the UE 101 and the UE 102 receiving a mobile communication service in the cell 100, the UE 102 is farther from the antenna 130 than the UE 101. Further, since the UE 102 is subject to large interference from a central antenna of the cell 120, the data rate supported by the cell 100 for the UE 102 is relatively low.
When each of the cells 100, 110, and 120 independently provides a mobile communication service, a Reference Signal (RS) for channel estimation is transmitted in order to measure a downlink channel state in each cell. Further, in the case of a 3GPP LTE-A system, a UE measures a channel state between an eNB and the UE by using a Channel Status Information-Reference Signal (CSI-RS) transmitted by the eNB.
The prior art takes allocation of only one CSI-RS to a particular UE into account and does not consider a multiple CSI-RS allocation situation for CoMP transmission, thereby allowing simultaneous transmission in multiple eNBs. The prior art does not disclose an allocation method of Interference Measurement Resource (IMR) to enable a UE to measure various interference situations.